As it is known, sometimes it is necessary to temporarily remove joint prostheses, for example as a result of the onset of infections in the respective implant area. Moreover, an infected prosthesis or a prosthesis extracted from an infected area cannot be immediately replaced with a new prosthesis, but one must first treat and eliminate the infection with suitable antibiotic drugs.
It should then be noted that during the period required for the antibiotic treatment, the joint space wherein a new joint prosthesis is to be implanted must, of course, be kept unchanged, so as to prevent the shortening of the tissues, the atrophy of the joint and the loss of muscle tone.
In this regard, spacer devices are used, which are intended to be temporarily implanted at the joint area of a patient for replacing a prosthesis and for maintaining the size of the joint area itself before reimplanting a second prosthesis.
The spacer device has the function of maintaining the joint spaces as well as curing the bone infection by releasing amounts of antibiotic in the infected area. As regards the second function now indicated, the spacer can treat the on-going infection by releasing antibiotic in a targeted manner and in infinitesimal quantities, while the application of even high doses of antibiotic, but with methods that do not involve the use of spacers, such as washing the infected area with solutions of high-dose antibiotics, does not allow obtaining the same results.
In fact, studies carried out in the field have revealed that the bone tissue absorbs in a concentrated manner all the (even a few) antibiotic molecules daily released by the spacer. This naturally occurs if the antibiotic is released by the spacer in contact with or near the bone tissue, in which case the amount of antibiotic reaches locally the effective concentration to eradicate the infection. For this reason, it is essential that the spacer extends across the whole infection area, this meaning that if the infected prosthesis is a long prosthesis, a long spacer will be used and, whether the infected prosthesis is of the short type, a short spacer will be used. Should a short spacer be placed where a long prosthesis was previously implanted, part of the bone would not be treated with antibiotic, in this way letting bacteria proliferate.
Spacer devices are usually made of bone cement and with the appropriate size, extemporaneously or prior to their positioning, which greatly increases the duration of the implant operation and also sometimes involves the use of toxic substances.
Pre-formed spacer devices have also been proposed, which cannot be adapted from patient to patient, with the obvious consequence that, in most cases, it is very difficult to guarantee patients a good mobility of the joint before reimplanting the definitive prosthesis.